Keep in mind I've been riding for a lot of years. Also keep in mind that I'm only relatively recently, ATGATT.
My ex introduced me to the sport bike world. When I asked her the definition of a "squid" she said it came from the fact they go "splat" when they hit something. Outside of birthing my son, that may be the best thing she's ever done for me.
In my opinion the definition follows through. I've never seen a geared-up rider doing things I consider to be stupid, on the interstate.
It's always the guy with a distinct lack of gear, doing the stupid stuff. Consequently, whenever I see a rider lacking in gear, especially on a sport bike, that person to me is a squid.
It doesn't matter if they are the safest person on the road. They go "splat" when they hit something.
I also extend that to the plethora of Harley riders around here. I've seen them do some really stupid things, though most are pretty tame. Still, no gear at all. Splat.
Have you ever noticed that? It's never the geared-up guy doing the stupid stuff. Squids do stupid stuff. Squids also do not wear all the gear, they go splat.
So, in my opinion, what is a squid? It begins with the lack of the gear, that most anyone would agree, helps to limit the splat. It continues when that same person does dumb things without said gear.
How come the cool guys in the vids, doing the stunt shows wear limited gear? Because the gear isn't cool. They're extremely skilled squids, but they're still squids.
Ask instead what is a non-squid. The non-squid is geared up and perhaps riding hard. But not overtly endangering anyone else. The non-squid recognizes the fact that they are riding hard and the gear is the answer to the very possible down, if they push it too far.
The lack of care, for the unforeseen consequences of what we are doing, is what makes a squid. The evidence is pretty damning. Those who don't care, who think being cool is more important than being intelligent, are squids.